An overhead carriage has been known which has a running portion placed inside a rail laid on the ceiling and an article placing portion provided outside the rail (see the Unexamined Japanese Utility Model Application Publication (Jikkai-sho) 60-161664). This carriage is placed so as to run at a height position where it normally does not come into contact with an operator. The carriage also has a safety device that detects an obstacle entering a running route of the carriage and stops the carriage when detecting an obstacle.
The term “running route” as used herein refers to the whole space through which the carriage passes. A space through which the running portion passes is covered with the rail, whereas a space through which the article placing portion passes is exposed to the exterior. The safety device is actuated not only when an operator crosses the running route but also when, for example, for replacement of an article processing device, an obstacle such as the processing device is transported across the running route. As such a safety device, an obstacle sensor such as a reflective optical sensor is mounted on the carriage.
An obstacle suddenly entering the running route may come into collide with the accidentally passing carriage (article placing portion), or even if the carriage is running at a position located away from the obstacle entry position, such a collision may occur when the carriage approaches the object but the breaks fail to be applied in time. Thus, when any obstacle possibly crosses the running route, the carriage is not operated. However, this may disadvantageously reduce carrying efficiency. That is, a problem to be solved by the present invention is that an exposed portion of the running route of the carriage (space through which the carriage passes) may cause an obstacle to enter the running route.